1. Field of the Invention
The present invention relates to a stator for a rotary electric machine used, for example, as an electric motor or a power generator in a vehicle, and a method of manufacturing the stator.
2. Description of the Related Art
Various types of rotary electric machines are used for electric motors and power generators mounted in vehicles, and the like. A type of rotary electric machine is known that includes a ring-shaped stator core and a stator coil as a stator for the rotary electric machine. The stator core has a plurality of slots arranged in a circumferential direction. The stator coil is wound around the slots in the stator core. In the stator, the stator coil is fixed to the stator core using an impregnating material, such as varnish, to ensure vibration resistance characteristics of the stator coil.
Various techniques for ensuring vibration resistance characteristics are known. For example, JP-A-2008-109733 discloses a method in which the impregnating material is dripped from a coil end section side of the stator coil projecting from an axial-direction end surface of the stator core, thereby impregnating the inside of the slots. JP-A-2006-262541 discloses a method in which a portion of the stator core is modified and the slots are expanded. The entire work is then immersed in an impregnating material bath and impregnated with the impregnating material.
A type of stator core is known that is not provided with a shoulder section projecting in a circumferential direction on a teeth tip, to improve space factor of the coil within the slots. In a stator core such as this, when the method disclosed in JP-A-2008-109733 is used, the impregnating material cannot be retained anywhere because the shoulder section is not present on an inward radial-direction side of an innermost-diameter-side coil of the stator coil. As a result, the innermost-diameter-side coil cannot be fixed to the stator core with certainty.
In the method disclosed in JP-A-2006-262541, a problem occurs in that performance deteriorates as a result of increased magnetic resistance in the slot expansion section. In addition, a problem occurs in that, when the entire work is immersed, the impregnating material is deposited in areas in which the impregnating material should not be deposited (such as an inner peripheral surface of the stator core that may interfere with a rotor, or an engaging section or a fastening surface between the stator core and a case member).
A coil wire positioned on the innermost-diameter side within the slots is required to be fixed with certainty. Therefore, the following can be considered: the stator core around which the stator coil is wound is disposed such that its axial line is in a horizontal direction, and the impregnating material is dripped from the inner peripheral side of the stator core while the stator core is rotated around the axial line, thereby impregnating the inside of the slots. However, in this instance, the following issues arise.
In this instance, the back end of the slots in an outward core-diameter direction can be impregnated with the impregnating material by centrifugal force. However, because the impregnating material does not easily flow in a core-axis direction, the area wetted by the impregnating material decreases the closer the coil wire is to the inner diameter side, and fixing strength is difficult to attain. In addition, Lorentz force due to leakage flux increases the closer the coil wire is to the inner diameter side. Therefore, when the fixing strength of the coil wire on the inner diameter side decreases, the inner-diameter-side coil wire may run out into a gap as a result of electromagnetic vibrations and interfere with the rotor.